Control system.



R. E. HELLMUND.

CONTROL SYSTEM. I APPLICATION FILED DEC. I8. 1914. RENEWED FEB. 2. 1918.

1,277,415. PatentedSept. 3,1918.

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UNITED STATES PATENT OFFICE.

RUDOLF E. HELLMUND, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0'WESTING-HOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENN-SYLVANIA.

CONTROL SYSTEM.

Specification of Letters Patent. Patented Sept. 3, 1918.

Application filed December 18, 1914, Serial No. 877,884. RenewedFebruary 2, 1918. Serial No. 215,226.

To all whom it may concern:

Be it known that I, RUDOLF E. I-InnLMUND, a subject of the GermanEmperor, and a resident of Pittsburgh, in the county of Allegheny andState of Pennsylvania, have invented a new and useful Improvement inControl Systems, of which the following is a specification.

My. invention relates to systems of control for electric motors, and ithas special reference to phase-regulating systems for induction motorsand the like.

In control systems of the type in question, namely, those comprisinginduction motors driven from alternating-current circuits and aphase-advancing machine connected to the secondary winding of theinduction motor and coupled to an auxiliary driving motor that is fedfrom the supply circuit, difliculty has been experienced in obtainingsuflicient phase-regulating effect at light loads without producingover-compensation under heavy load conditions. This statement isparticularly true of the class of phase advancers that have no statorex-, citing winding. Ideal conditions may be approached to a certaindegree by operating phase-advancers with relatively high flux densities,which, however, gives an effect that is undesirably limited in its rangeof operativeness.

The object of my invention is to provide means which shall be simple andinexpensive in construction and reliable and effective in operation, forautomatically varying the phase compensation in induction motors inaccordance with load conditions thereof, whereby the proper value ofcompensation may be automatically obtained at,

all loads.

According to my invention, I connect a speed-controlling field magnetwinding of the driving motor of the phase-advancer in series relation orotherwise with one or more phase windings of the primary winding of theinduction motor, whereby the driving motor and the phase-advancer run atrelatively high speeds at light loads and afford the requisite phasecompensation, but operate at relatively low speeds under heavy loadconditions, thereby preventing overcompensation in the induction motor.

In the accompanying drawing, Figure 1 and Fig. 2 are similardiagrammatic views of two-phase and three-phase control systems,respectively, that embody my invention; and Figs. .3 and 4 arediagrammatic views of modifications of similar portions of the controlsystems shown in Fig. 2 and in Fig. 1, respectively.

Referring to Fig. 1, the system here shown comprises a four-wire,two-phase supply circuit having the phases AA, BB; an induction motorhaving its two-phase primary winding 'P suitably connected to the supplycircuit and having a phase-wound secondary winding S; a regulatingresistor R suitably connected in the secondary winding circuit; a phaseadvancer PA that is associated with the secondary winding S in a mannerto be described; and an auxiliary driving motor DM for the phaseadvan'cer PA.

The phase advancer may be of any familiar type,such as the well-knownphaseadvancer having no stator exciting winding, and is provided with arotatable armature member 1 upon the commutator cylinder of which aplurality of brushes 2 bear at the 90 points. A plurality ofshort-circuiting switches 3 are preferably disposed intermediate thephase advancer and the regulating resistor R to short circuit thephaseadvancer under starting conditions of the induction motor. Thedriving motor DM may be coupled to the phase-advancer PA in any suitablemanner, as by a shaft 4, and comprises a conunutator-type armature 5that is connected across the phase BB of the supply circuit; ashort-circuited compensating windingfi of a familiar type;

and a main exciting field winding 7 that is connected in series with oneof the phase windings of the primary winding P of the induction motoracross the other phase AA of the supply circuit.

Inasmuch as the field winding 7 is highly inductive relative to thearmature winding proximately in phase with the armature current, andconditions are suitable ior proper operation of the driving motor.

Assuming the machines shown to be at a stand-still, the operation of thesystem may be set forth as follows: The short-circuiting switches 3 arepreferably initially closed to short-circuit the phase-advancer, whilethe induction motor is accelerated. The regulating resistor R issuitably connected in the secondary circuit to provide proper startingtorque, in accordance with familiar practice. The primary winding P ofthe induction motor may then be connected to the supply circuit inaccordance with any familiar practice to gradually bring the inductionmotor up to normal speed. The aux iliary driving motor DM may also bestarted into operation and brought up to speed in any suitable manner;and the short-circuiting switches 3 may then be opened to 0perativelyconnect the phase-advancer to the secondary winding S of the inductionmotor. Under light load conditions on the induction motor, it will beappreciated that the exciting field winding 7 of the driving motorcarries a relatively small current and the speed of the motor is,consequently, relatively high. The phase-advancer, therefore, supplies arelatively high degree of phase compensation to the secondary windingcircuit, and the de-' sign of parts may be such as to providesubstantially the exact amount of phase compensation desired, as will beunderstood. ()n the other hand, under heavy load conditions on theinduction motor, the current traversing the exciting field winding 7 ofthe driving motor is relatively large. The degree of compensationprovided by the pl1aseadvancer is thus maintained at a desirably lowvalue, and over-compensation of the induction motor under heavy loadconditions is effectively prevented.

Referring to Fig. 2, the system shown comprises a three-phase supplycircuit having the phase conductors G, D, E; a threephase inductionmotor having a primary winding P and a secondary winding S :1 regulatingresistor R that is connected in the secondary winding circuit, asdescribed in connection with Fig. 1; a three-phase phase-advancer PAthat is associated with the secondary winding S in the usual manner; andthe auxiliary driving motor DM.

The phase advancer PAS corresponds to the machine PA shown in Fig. 1,having a suitable armature S that is provided with a plurality ofbrushes 9 for appropriate con ncction with the respective phase windingsof the secondary winding S The driving motor DM has its armature 5connected across the phase D, E, while the exciting field winding 7 hasone terminal connected to the conductor C and the other terminalconnected to one of the phase windings of the primary winding P Thedesign of the driving motor DM is such as to provide sat isiaetoryoperation with'its rotor and stator windings connected as shown.

Inasmuch as the operation of the system shown in Fig. 2 correspondsexactly to that of the system illustrated in Fig. 1, nofurtherexposition thereof is deemed necessary.

Reference may now be had to Fig. 3, wherein another type of drivingmotor DM is illustrated. The driving motor DM comprises the excitingfield winding 7 that is connected to the primary winding P of theinductionfmotor in the same manner as that shown in. Fig. 2; acommutator type armature winding 10 that is provided with a pernianentshort-circuiting conductor 11 and an auxiliary compensating winding 12that is connected across the phase D, E, of the sup ply circuit, as wasthe armature 5 in the System illustrated iirFigQ'Q. This type of drivingmotor may be termed an indirectly fed motor, inasmuch as the E. M. F.impressed upon the armaturelO 1s inductively transferred thereto throughthe agency of the compensating field winding 12.

The operation out the driving motor DM under light and heavy loadconditions, respectively, is similar to that described in connectionwith the driving motor DM that is illustrated in the other figures.

In case undersirable operating results are obtained in any case frompossible unbalancing of the loads on the respective phases by reason ofthe inclusion of the auxiliary motor field winding in the circuit ofonly one phase winding of the induction motor, the system shown in Fig.i may advantageously be employed. The system in question may comprisethe two-phase supply circuit AA, BB, the induction motor, and thephaseadvancer PA, as illustrated in Fig. 1, the secondary winding S andthe phase-advancer PA being omitted from the drawing for the sake ofsimplicity and convenience; and a driving mot-or DM The motor DM isshown as comprising'a two-phase commutator type armature 13, one set ofoppositel ydisposed brushes 14 of which is connected through ahalf-section 15 of an auxiliary .field winding across the phase AA ofthe supply circuit, and another set of brushes 16 that are disposed inquadrature relation to the brushes 1% is connected through the otherhalf section 15 of the auxiliary field winding to the phase 13B; and amain or exciting field winding having its half-sections 17 and 17connected to the phases AA and BB, respectively, through thecorresponding phase windings of the induction motor primary winding P.The purpose of the main :field windings 17 and 17 is to provide excitingcurrent for the driving motor in accordance with the load currentscarried by the primary windings of the induction motor, while theauxiliary field windings 15 and 15 function isto neutralize themagnetizing eflect of armature reaction.

The operation of the system just described, considered in the light ofthe exposition relating to Fig. 1,is deemed sufiiciently obvious topreclude the necessityof further explanation.

I do not wish to be restricted to the specific circuit connections orarrangement of parts herein set forth, as various modifications thereofmay be made without departing from the spirit and scope of my invention.I desire, therefore, that only such limitations shall be imposed as areindicated in the appended claims.

I claim as my invention:

1. The combination with an alternating current suppy-circuit, and aninduction motor having a primary winding adapted for connection theretoand vhaving a secondary winding, of a phase-advancer connected to saidsecondary winding, and a commutator motor for driving saidphaseadvancer, fed from said supply circuit and having a speed-varyingfield magnet Wind- .ing excited in accordancewith the load on theinduction motor, whereby the proper values of phase compensation in theinduction motor are automatically obtained at all loads.

2. In a power-factor control system for an induction motor, thecombination with a secondary winding, of a rotary phase advancerconnected thereto, a commutator motor for driving said phase advancer,and energizing means between the exciting-fieldproducing means of saidcommutator motor and the primary supply leads of said induction motor,whereby the exciting field and the speed of said commutator motor varywith the load on said induction motor.

3. The combination with a source of alternating current, of an inductionmotor of the wound secondary type, connections from said source to theprimary winding of said motor, a phase converter, connections from thesecondary winding of said motor to said phase converter, a driving motorof the alternating current commutator type mechanically coupled to saidphase converter, means for energizing the armature winding of saidcommutator motor, and energizing means between the supply leads of saidinduction motor and the exciting-field-producing means of said drivingmotor, whereby the speed of the latter and consequently the angle ofphase shift of said phase converter varies with the load on saidinduction motor.

4. The combination with a source of alternating current, of an inductionmotor of the wound secondary type, connections from said source to theprimary winding of said motor, a phase converter, connections from thesecondary winding of said motor to said phase converter, a driving motorof the alternating current commutator type mechanically coupled to saidphase converter, connections from a portion of the windings of saiddriving motor to said source,

and series type connections from other the alternating currentcommutator type,

mechanically coupled to said phase converter, connections from thearmature winding of said commutator motor to said source, andconnections for inserting the main field winding of said commutatormotor in one of the supply leads of said induction motor.

6. The combination with a dynamo-electric machine, of an auxiliarygenerator connected thereto and adapted to supply substantially wattlessexcitation only thereto, a driving motor for said auxiliary generator,and means for varying the voltage of said exciting means byautomatically adjusting the speed of said driving motor in accordancewith the load of said alternating current machine.

7. The combination with a dynamo-elec tric machine, of an auxiliarygenerator connected thereto and adapted to supply substantially wattlessexcitation only thereto, driving means for said auxiliary generator, andmeans for varying the voltage of said exciting means by automaticallyadjusting the speed of said driving means in accordance with the load ofsaid alternating current machine.

8. In the combination with a main electric motor of an excitinggenerator therefor adapted to supply substantially a leading 'wattlessexcitation only thereto, a driving motor for said generator, and meansfor excitingthe main field winding of said driving motor in accordancewith the load of said main motor.

9. The combination with an induction motor of the wound secondary type,of any exciting generator connected to the secondary winding thereof, adriving motor of the alternating current commutator type therefor, meansfor exciting the main field subscribed my name this 10th day of Dec.

Winding of said driYing motor in accordance 1914. mth the load of saldlnductlon motor, and

, E RUDOLF E. HELLMUND. means ior lmpressmg a substantmlly con- I r Vstunt eloctromotive force upon a Working Vitnesses: Winding of saiddriving motor. JOHN S. DEAN, In testimony whereof, I have hereunto13,13. HINES.

Cophs of this patent may be obtained tor five cents each, by addressingthe Commissioner 0! Patentz.

Washington, D. 0.

